2D Arbitrary Shape-Selective Excitation Summed Spectroscopy (ASSESS)

Qin Qin, John C. Gore, Mark D. Does, Malcolm J. Avison, Robin A. De Graaf

Research output: Contribution to journalArticlepeer-review


Conventional single-voxel localization for MR spectroscopy (MRS) is restricted to selecting only rectangular-shaped regions of interest (ROIs). The complexity of tissue shapes of interest and the desire to maximize the signal-to-noise ratio (SNR) while minimizing partial-volume effects require more sophisticated localization techniques. A group of spatially selective RF pulses are proposed in this work for the measurement of spectra from regions of arbitrary shape based on using a radial trajectory in k-space. Utilizing a single k-line per excitation results in a broad spectroscopic bandwidth. However, spatial localization accuracy is compromised for nutation angles > 10° because of the small-tip-angle approximation of the Bloch equations. By interleaving multiple radial k-lines per excitation with nonselective refocusing pulses, one can achieve accurate localization for nutation angles up to 90° while simultaneously maintaining the spectral bandwidth. The technique is described and compared with existing localization methods, and in vivo results are demonstrated.

Original languageEnglish (US)
Pages (from-to)19-26
Number of pages8
JournalMagnetic resonance in medicine
Issue number1
StatePublished - Jul 2007
Externally publishedYes


  • Arbitrary shape localization
  • Bandwidth broadening
  • Concatenation
  • In vivo MRS
  • Radial trajectory in k-space

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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